1. Field of the Invention
This invention relates to a support system for the solid propellant grain in a rocket motor, and more particularly, to a support system having particular utility for supporting the unpressurized propellant grain of a rocket motor in a high acceleration environment. Typically, the upper stages of multistage interceptor rockets are exposed to such an environment.
2. Description of the Prior Art
Solid propellant rocket motors utilize a high strength cylindrical case having a thin wall into which the propellant grain is cast and cured with a layer of a suitable insulating material positioned between the propellant grain and the interior wall of the case. The case is closed at the forward end thereof and has a nozzle at the aft end for the emission of exhaust gases. For relieving the propellant grain of stress encountered in a high axial acceleration environment, it has been the practice to provide a split flap hinge support structure at the forward end of the case, interiorly thereof, for attaching the forward end of the propellant grain thereto.
Conventional stress relieving split-flap hinge structures for attaching the forward end of the propellant grain to the inner forward end of the rocket motor case include materials comprising chopped fibers of an aramid, glass, asbestos, etc. in a rubber matrix. Aramids include poly (benzamides) and the family of materials marketed by E.I. DuPont de Nemours & Company of Wilmington, Delaware, under the trademark KEVLAR. These materials usually have a tensile modulus, at room temperature and at a strain rate of 0.74 inches/inch/minute of less than eight thousand pounds per square inch (psi). Tensile modulus, also referred to as Young's modulus, generally is designated by the symbol "E". For the conventional or prior art stress relieving split-flap structures described, the tensile modules thus may be expressed as E&lt;8,000 psi.
Stress relief for the propellant grain in a rocket motor can be achieved with grain support tubes, contoured slots, low stress configurations, or internal grain support. Such arrangements for achieving stress relief in the propellant grain have disadvantages, however, of reducing the loading density, or mass fraction, in the rocket motor and/or of adding weight. Mass fraction is the ratio of the mass of the propellant grain in a rocket motor case to the total mass that could be put in the case if it were completely filled.
A need exists for improvement in the systems or structures provided for supporting the unpressurized propellant grain of a rocket motor having an axisymmetric geometry in a high axial acceleration environment that minimized the amount of propellant lost with minimal inert weight penalty. The present invention was devised to fill the technological gap that has existed in the art in this respect.